Three years later in 1972, Apollo 17 astronaut Eugene Cernan stood on the lunar surface in what would be mankind's last excursion to the Moon to-date.

Reporting back to Earth, he said: "[Apollo] has opened for us a challenge of the future. The door is now cracked, but the promise of the future lies in the young people.

"Not just in America, but the young people all over the world learning to live and learning to work together."

The Nixon administration heeded his words.

Three months after Apollo 17 returned home in December 1972, Again, Nixon ordered the distribution of Moon rocks to 135 foreign heads of state, the 50 US states and their provinces.

The Moon rocks were labelled sample 70017. Each was encased in an acrylic button mounted to a plaque, with the intended recipients' flag, which had also been flown to the Moon.

A letter, signed by President Nixon and dated March 21, 1973, accompanied each Moon rock.

"On behalf of the people of the United States I present this flag, which was carried to the moon... and its fragment of the moon obtained during the final lunar mission of the Apollo program.

"If people of many nations can act together to achieve the dreams of humanity in space, then surely we can act together to accomplish humanity's dream of peace here on earth," it read.

The missing Moon rocks

Upon being gifted, each Goodwill Moon rock became the property of the recipient - and therefore no longer subject to being tracked by NASA.

Whereas other lunar samples' locations are well documented by NASA to this day, as the years went by the gifted Apollo 17 lunar rocks started to go missing.

Today, of the 135 Apollo 17 rocks given away to other nations, the whereabouts of only 25 of them are known. An even vaguer fate befell the 134 distributed Apollo 11 rocks. The locations of fewer than a dozen are today recorded.

Apollo 17's Eugene Cernan

Earlier this year, declassified US State Department documents came to light revealing the fates of some of the Moon rocks.

It emerged that many recipient nations claimed to have never heard of the rocks, five were handed to African dictators now dead or deposed and, among the others, Malta's rock was stolen and Pakistan's is missing.

It is generally accepted that details surrounding the Moon rocks were so vague because nobody really expected Apollo 17 to be mankind's last lunar excursion.

Today, the rocks remain missing. Moreover, each rock is now subject to the laws of public gifts for whichever country it was given to.

In most cases -the United States included -public gifts cannot be legally transferred to individual ownership without the passage of additional legislation.

Needless to say, with no further US Moon excursions planned, the missing rockswould be highly valuable, and as sought-after as they are elusive.

At Paul Fraser collectibles, we currently have some valuable and elusive space memorabilia of our own.

Ajoint photo of Apollo 11's Neil Armstrong, Buzz Aldrin and Michael Collins, separate individual signed photos by each of them and, incredibly,Michael Collins's Apollo 11 flight suitcan each be part of your space collection.